Various attempts have been made in the packaging industry to stabilize large-volume boxes, pliable-walled, i.e., semi-rigid, folding containers or foldable bulk containers (FIBC).
It is primarily the action of the side-wall surfaces, which tend to bulge beyond their predetermined surface area, which should be prevented. In particular, in the case of outer packaging having compliant wall surfaces, it could be established that these did not withstand the pressure of free-flowing dry products.
It was possible to avoid the above-described disadvantages of the boxes to a sufficient extent by providing an octagonal insert.
In the case of flexible containers, which are usually produced from strong fabrics (FIBC), additional wall parts, which were sewn in over the corners, had an advantageous pressure-relieving effect. However, in many cases, as a result of product protection, use is to be made of film liners which, with an inner chamber formation of the container, cannot be designed appropriately as far as the walls are concerned. It has thus been necessary, in such cases, to stabilize the film liner itself. The low wall thickness of films meant that only welding was considered for production purposes. The stabilization has been achieved by a round strap (inner ring) with a particular restraining force being welded in separately as shown in EP-A1-0 276 878 ("the EP '878 reference"). In the method of the EP '878 reference, an already preformed flexible liner has to be opened somehow in order to weld an inner ring to the insides of the film. This laborious, and not always reliable, adaption operation is indeed avoided by the production method disclosed in U.S. Pat. No. 5,618,255, because the strap and outer bag are first of all connected in the open, flat state, but the subsequently necessary formation of a gusseted tube of a number of meters in width and length has proven to be obviously difficult. The concluding formation of the inlet and outlet stub requires separate production.
All the production methods which have been devised up to now for this purpose are thus extremely time-consuming and thus costly. In many cases, it is not possible to achieve the necessary strength for a weld seam for the event where the latter is subjected to tensile stressing.